Additional topic for virtual interim

I was thinking we may want to add this issue to the virtual interim agenda
after all: https://github.com/w3c/webrtc-pc/issues/1128

The issue is essentially: There are situations where the "track" event will
fire with a randomly generated track ID, as opposed to the track ID from
SDP.

Not everyone may be aware of this consequence (it's come up before
<https://github.com/w3c/webrtc-pc/issues/570>), so it would be nice to make
a definitive decision about whether this behavior is acceptable. I only
remember discussing it informally at TPAC.